Java 17 Recipes

 How It Works
Lambda expressions have access to the variables located within the enclosing class. 
Thus, a lambda expression contained within a class method can access any instance 
variables of the enclosing class. No additional scope is added to a lambda expression, so 
it can access fields, methods, and local variables of the enclosing scope. In the solution, 
the lambda expression contained within the lambdaInMethod() method can access all 
of the fields that are declared within either class. This is because both the inner and 
outer classes enclose the lambda. One thing to note is that if an inner class contains an 
instance variable of the same name as a variable that has been declared in the outer 
class, then the lambda uses the variable of its enclosing class. Therefore, in the solution, 
the InnerClass CLASSA field is accessed from within the lambda expression rather than 
the outer class reference.
Local variables referenced from within a lambda expression must be either final or 
effectively final. An error occurs when a lambda expression attempts to access a variable 
that was changed within the context of an enclosing method. For instance, suppose that 
the method in the solution was changed to the following.
void lambdaInMethod(String passedIn) {
String METHODA = "Method-level A";
passedIn = "test";
Consumer l1 = x -> {
System.out.println(x);
System.out.println("CLASSA Value: " + CLASSA);
System.out.println("METHODA Value: " + METHODA);
System.out.println(passedIn);
};
l1.accept(CLASSA);
l1.accept(passedIn);
}
Note that the string passed into lambdaInMethod() is assigned a new value just 
before the lambda expression is invoked. Therefore, the passedIn variable is no 
longer effectively final, and lambda expressions cannot introduce a new scope level. 
Consequently, the lambda expression does not have access to the passedIn variable 
from within the context of the expression.
ChapTer 6 LaMbda expressIons

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